Using OS MasterMap and Transverse Mercator projection in ArcMap?

Question

I'm trying to use the Transverse Mercator projection in ArcMap, but cannot seem to locate it in the coordinate system list.

I'm very new to GIS and ArcMap.

I'm going to try to use some data from OS Mastermap, which I believe is in the Transverse Mercator projection.

When I look at that projection, it looks very different to the one I get in ArcMap when I select WGS 1984 World Mercator, so I think I'm doing something wrong. I can't see Transverse Mercator in the coordinate system list either.

What I'm hoping for taken from wikipeia, what I have:

(And I think my datum is wrong as is is saying D_WGS_1984 and not OSGB36.)

How do I set up ArcMap to be in the Transverse Mercator projection?

Answer 1

I would assume that OS MasterMap is in British National Grid, EPSG:27700. British National Grid (BNG) uses transverse Mercator with parameters specific to the UK.

Try typing that number (without EPSG:) into the search box of the data frame properties' coordinate system tab. You should also click the Transformations button and see if you need to set a transformation from OSGB 1936 (the geographic coordinate reference system / geodetic datum) that BNG uses to WGS 1984 or ETRS 1989 or whatever else your data or map is using.

Background information: Transverse Mercator is a map projection. You need to set its projection parameters to have values that make sense for the data, and use a geographic coordinate reference system that makes sense for the data as well.